Clamshell pipe lathes generally comprise first and second semicircular halves that are designed to be joined to surround a pipe to be machined. The resulting annular assembly includes a stationary ring portion that becomes clamped to the pipe and an abutting rotatable portion including a gear ring attached to the stationary ring portion for rotation about the concentrically disclosed pipe. A motor is operatively coupled to the assembly and includes a gear drive designed to mesh with the gear ring on the rotatable portion of the lathe. Bearing assemblies are typically disposed between the stationary ring portion and the rotatable portion. One conventional bearing system used in clamshell pipe lathes is a V-groove guide bearing system. These bearing systems are self-contained units holding small ball bearings that rotate on a fixed axis and transfer loads from the rotatable portion to the stationary portion of the lathe.
The size and space taken up by V-groove guide bearings, compared to the actual bearing size, is disproportional and limits the number of bearing units and/or elements that can fit into the pipe lathe. In the V-groove guide bearing system each bearing unit or element is independently adjustable. If all of the bearing units or elements are not properly adjusted some of the bearing units or elements may not be in proper contact within the system, reducing bearing support and cutting performance. Further, V-groove guide bearings have a limited carrying capacity for heavy axial loads, since they are only intended to carry radial loads. In addition, V-groove guide bearings have a tendency to form unwanted witness lines in the surface of the pipe caused by the rotational portion coming in direct and repeat contact with the fixed bearing element location at the split-line where the two halves join.
Another type of conventional bearing system used in clamshell pipe lathes is an adjustable sliding bearing. This system provides high radial and axial thrust loads and superior surface finishes. However, this system is limited because it cannot scale up to larger pipe sizes and has to operate at slower speeds due to excessive heat generated by the sliding surfaces. This excessive heat causes the material to change in size, which changes the clearances between the bearing surfaces. Further, to overcome overheating issues, design modifications to these conventional sliding bearing systems have resulted in added weight and size, which makes the pipe lathe harder to use and more costly. In addition, this bearing design, like the V-guided bearing design, requires significant area to be dedicated to accommodate the placement of components within their adjoining stationary rings, thus reducing the overall clamping strength of the overall structure.